This invention relates to the art of wireless communication, and more particularly, to a method of improving the quality of data communication at the time of handoff of a call from one base station to another.
Prior art wireless systems during wireless data transmission typically rely on the transport layer, or layer-4 in the International Standards Organization (ISO) Open Systems Interconnection (OSI) seven layer reference model for data communications to insure reliable data transfer end-to-end for a data call. Therefore, if a data packet is lost due to a handoff of a wireless terminal from a first base station to a second base station during transmission of the packet, some layer-4 protocols will cause the retransmissions of the packet from its source all the way through the network to the destination. This leads to network delays and additional loading of the network. Other layer-4 protocols are not designed to retransmit lost packets, resulting in a gap in the data at the destination. Thus, with either protocol type there is a penalty associated with relying on layer-4 to handle packets lost as a result of a handoff.
We have recognized that the penalties associated with relying on layer-4 to handle packets lost as a result of a handoff can be reduced, in accordance with the principles of the invention, by forwarding, in response to a handoff request from a first base station to a second base station, at least one layer-2 frame of a layer-3 packet that is destined to/from the wireless terminal that has been passed down from layer-3 to layer-2, and so is indicated to have been transmitted at layer-3 even though not all of the layer-2 frames of the layer-3 packet have actually been transmitted. In one embodiment of the invention, each of the at least one layer-2 frames may be encapsulated together in a special layer-3 packet that is transferred from the first base to the second base station in the usual manner of inter-base-station communication. Advantageously, packets are not lost at layer-4 due to handoffs. Thus, layer-4 retransmissions are not required, and so delays in the network are reduced. Furthermore, if only the layer-2 frames that were not transmitted over the air to the wireless terminal by the first base station are transferred to the second base station, a savings may be had in use of the air interface.